1. Field of the Invention
The present invention relates to rotary connectors for electrically connecting an electrical device disposed in a rotor section of a steering apparatus and an electrical device disposed in a stator section thereof. In addition, the present invention also relates to connecting structures of a flexible cable and a lead block used in the rotary connectors.
2. Description of the Related Art
Conventionally, rotary connectors which include a pair of housings which are concentrically disposed and are linked together so as to be rotatable relative to each other; a flexible cable which is contained in a space between the housings in such a manner that the flexible cable is able to be wound and be loosened therein; and one or two lead block(s) which is/are connected to one or both end(s) of the flexible cable, are known in the art. The end of the flexible cable to which the lead block is connected is fixed to one of the housings at a predetermined position and is electrically connected to the external environment via lead wires or an external connector connected to the lead block. In addition, the end of the flexible cable to which the lead block is not connected is directly fixed to one of the housings at a predetermined position and is electrically connected to the external environment. One of the housings is movable, and the other one is immovable.
In the rotary connectors constructed as described above, the immovable housing is fixed to a steering column of a steering apparatus, and the movable housing is fixed to a steering wheel thereof. In addition, both ends of the flexible cable are individually connected to electrical components disposed in the steering column and in the steering wheel. Thus, the rotary connectors are used to form an electrical connection for air bag systems, horn circuits, etc.
The flexible cable is constructed by arranging a plurality of conductive wires in a parallel manner and sandwiching the conductive wires with a pair of insulating films, and has a band-like shape of a predetermined length. In addition, the lead block is constructed by connecting a plurality of joint bars formed of a conductive material with an insulating supporter. The joint bars are arranged with the same pitch as the pitch between the conductive wires.
The flexible cable and the lead block are connected to each other by the following process. First, a part of one of the insulating films in the flexible cable is removed so that the conductive wires are exposed at the remaining insulating film at an end of the flexible cable. Then, the thus exposed conductive wires are connected to the joint bars in the lead block using a connecting device such as an ultrasonic welding device, etc. When the ultrasonic welding device is used as the connecting device, a welding tip installed in the ultrasonic welding device is pressed against the flexible cable from above, so that the conductive wires and the joint bars, which oppose each other, are welded pair by pair.
When the welding tip is pressed against the flexible cable from above and a transmitter installed in the ultrasonic welding device is activated, ultrasonic energy transmitted from the transmitter is concentrated at the pressing part of the welding tip. Then, the ultrasonic energy is converted into heat, by which a part of the insulating film melts and one conductive wire and one joint bar are welded.
As described above, the conductive wires in the flexible cable and the joint bars in the lead block are not welded simultaneously, but are welded pair by pair. When a pair including one conductive wire and one joint bar is processed by ultrasonic welding, the insulating film partly melts at regions surrounding the welded part. Thus, even when the conductive wires and the joint bars are accurately positioned in advance, a displacement occurs between the conductive wires and the joint bars which have not yet been processed by the ultrasonic welding. When the conductive wires and the joint bars are sequentially connected by performing the ultrasonic welding to one pair, then to the adjacent pair, and so forth, partial deformation of the flexible cable due to the melting of the insulating film accumulates every time a pair is welded. Thus, the largest amount of displacement occurs at the pair which is welded last.
Accordingly, in a connecting structure of a flexible cable and a lead block in which an allowable displacement is small, for example, when the widths of the conductive wires and the joint bars are small or when the number thereof is large, it becomes difficult to establish adequate electrical connections between the conductive wires and the joint bars. Thus, connection failures easily occur. In addition, in order to prevent the connection failures, the connecting parts of the conductive wires and the joint bars must be fixed with a special jig. Accordingly, the efficiency of connecting the flexible cable and the lead block is reduced, and the cost of the rotary connector is increased.
Since the number of electrical components installed in a steering apparatus has recently increased, it is strongly demanded that the number of conductive wires in the flexible cable of the rotary connector is also increased without increasing the width of the flexible cable. In order to satisfy such a demand, the pitch between the conductive wires must necessarily be reduced. Accordingly, the above-described disadvantages have become increasingly serious.
The above described disadvantages occur not only in cases in which the ultrasonic welding device is used, but also in cases in which other welding devices or soldering devices are used, as long as the conductive wires and the joint bars are welded pair by pair.
In view of the above-described situation of the conventional technique, an object of the present invention is to provide a connecting structure of a flexible cable and a lead block in which conductive wires and joint bars are easily connected with increased accuracy. In addition, it is also an object of the present invention to provide a rotary connector including a flexible cable and a lead block having such a connecting structure.
In order to solve the above-described problems, a rotary connector according to the present invention includes a pair of housings which are concentrically disposed and are linked together so as to be rotatable relative to each other; a flexible cable which is contained in a space between the housings in such a manner that the flexible cable is able to be wound and loosened therein, and which is formed in a band-like shape by sandwiching a plurality of conductive wires with two insulating films; and a lead block which is connected to an end of the flexible cable and has such a construction that a plurality of joint bars which are conductive are connected by an insulating supporter. In a part of the flexible cable which is connected to the lead block, one of the two insulating films is removed so that the end portions of the conductive wires are exposed at the remaining insulating film, through holes being formed in the remaining insulating film at positions between the exposed conductive wires, and the exposed conductive wires being electrically connected to the joint bars at positions close to the through holes.
Accordingly, when a pair including one conductive wire and one joint bar is welded, the remaining insulating film partly melts. However, since the through holes are formed in the remaining insulating film at positions close to the positions at which the conductive wires and the joint bars are connected, the partial deformation of the flexible cable due to the melting of the insulating film can be absorbed by the through holes. Accordingly, the displacement between the conductive wires and the joint bars which have not yet been connected can be made zero or be reduced. Thus, adequate electrical connections can be established for all the conductive wires and the joint bars, and connection failures can be prevented.
In addition, a connecting structure of a flexible cable and a lead block according to the prevent invention includes a flexible cable which is formed in a band-like shape by sandwiching a plurality of conductive wires with two insulating films; and a lead block which has such a construction that a plurality of conductive joint bars are connected by an insulating supporter. In a part of the flexible cable which is connected to the lead block, one of the two insulating films is removed so that the end portions of the conductive wires are exposed at the remaining insulating film, through holes being formed in the remaining insulating film at positions between the exposed conductive wires, and the exposed conductive wires being electrically connected to the joint bars at positions close to the through holes.
Accordingly, since special jigs or operations for fixing the flexible cable are not required, the connecting. process of the flexible cable and the lead block can be made simpler, and the manufacturing cost of the rotary connector can be reduced. The number of the through holes formed in the insulating film may be determined in consideration of the amount of deformation which occurs in the connecting process. When the amount of deformation is large, the through holes may be provided between all the conductive wires, and when the amount of deformation is small, the through holes may be provided between only some of the conductive wires. In addition, the size of the through holes formed in the insulating film may be adjusted in consideration of the amount of deformation which occurs in the connecting process, within a range in which the shape and the arrangement of the conductive wires are not affected.
The through holes may be provided between all the conductive wires on the remaining insulating film and be arranged in a line. Alternatively, the through holes may be provided between only some of the conductive wires on the remaining insulating film.